1. Field of the Invention
This invention relates to a digital broadcasting system and a digital broadcasting method, and is applied to transmit programs from a primary transmission system such as a digital satellite broadcasting system to a secondary transmission system such as a cable television system. In detail, when a broadcast program is transmitted from a primary transmission system to a secondary transmission system, change information which indicates the content change of program is transmitted from the primary transmission system to the secondary transmission system a certain period of time in advance of the schedule time of a program corresponding to the change information so that the secondary transmission system can easily and quickly respond to the prolongation of air time of a program in broadcasting.
2. Description of Related Art
Heretofore, in the terrestrial broadcasting, the program switching is informed from a key station to network stations by use of net Q-data inserted in the vertical interval time code of video signal in advance so that network station can rearrange commercial programs.
On the other hand, in the digital satellite broadcasting system which is the primary transmission system, the program specific information (PSI), which is the selection reference of service, is broadcast at a certain time interval to broadcast the electronic program guide (EPG) so that a desired channel is selected easily from among many channels.
The PSI is the selection reference data for selecting a channel by use of video data and audio data, and consists of four tables: a program association table (PAT), a program map table (PMT), a conditional access table (CAT), and a network information table (NIT), and various descriptors. PAT, among these tables, is loaded with the packet ID of PMT and the packet ID of NIT corresponding to the channel number of the broadcast program (in this case, identical with the service ID (SID)), and PMT is loaded with the packet ID of video data and audio data which are components of respective programs.
The PSI is structured so that the packet ID to which video data and audio data of a desired program are assigned is easily detected by detecting a packet ID corresponding to the channel number of the desired program from the PAT after the packet ID of PMT is detected from PAT to detect PMT.
On the other hand, CAT is used for transmission of chargeable broadcast information. The frequency of transponder, which is physical information of the transmission line, is recorded on NIT. The PSI is structured so that broadcast by another transponder is received with reference to the NIT and a desired program is received resultantly when the program desired by a user is not broadcast by the transponder which is now being received.
On the other hand, the electronic program guide EPG is used for on-screen display of scheduled broadcast programs.
In the case of digital satellite broadcasting system, broadcast programs are transmitted from a primary transmission system which is a digital satellite broadcasting system to secondary transmission systems which are cable television systems like the relationship between a key station and network stations in the field of terrestrial broadcasting. In this case, the multi-channel service is provided from a digital satellite broadcasting system which is a primary transmission system and the multi-channel service is provided to viewers of a secondary transmission system which is a cable television provider.
However, when the broadcasting schedule is changed immediately before broadcasting due to prolongation of the air time in a digital satellite broadcasting system which is a primary transmission system, it could be difficult for the secondary transmission system side to respond easily and quickly to the prolongation of the air time of the primary broadcasting system unless the broadcasting schedule is changed in the cable television side which is a secondary transmission system because the program is broadcast according to the original broadcasting schedule in the secondary transmission system and the information is not transmitted smoothly from the primary transmission system to the secondary transmission system.
In such case, a method in which program switching is informed in advance by use of net Q-data as used in terrestrial broadcasting could be an alternative, but net Q-data inserted in the vertical interval time code can not be transmitted in the digital satellite broadcasting differently from in the terrestrial broadcasting. Another method in which program switching is detected with reference to the PSI could be an alternative, but the processing timing is too late when program switching is detected by the PSI because the PSI changes synchronously with the program switching. Yet another method in which the electronic program guide EPG is used could be an alternative, but it is difficult to respond to prolongation of air time.